1. Field of the Invention
The invention relates to an optical system for a microlithographic projection exposure apparatus, and to a microlithographic exposure method.
2. State of the Art
Microlithographic projection exposure apparatuses are used for producing microstructured components, such as, for example, integrated circuits or LCDs. Such a projection exposure apparatus comprises an illumination device and a projection lens. In the microlithography process, the image of a mask (=reticle) illuminated with the aid of the illumination device is projected, via the projection lens, onto a substrate (e.g. a silicon wafer) coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask structure to the light-sensitive coating of the substrate.
During the operation of a microlithographic projection exposure apparatus, there is a need to set defined illumination settings, i.e. intensity distributions in a pupil plane of the illumination device, in a targeted manner. Alongside the use of diffractive optical elements (so-called DOEs), the use of mirror arrangements is also known for this purpose, e.g. from WO 2005/026843 A2.
Such mirror arrangements comprise a multiplicity of micromirrors that can be set independently of one another.
Furthermore, it is known from WO 2009/100862 A1 both to set different illumination settings with regard to the polarization distribution by temporal correlation between, firstly, a device for changing the polarization state, such as e.g. a Pockels cell or Kerr cell, and, secondly, a mirror arrangement comprising mirror elements that can be set independently of one another, the mirror arrangement being situated in the illumination device, and to realize an electronic changeover between such differently polarized illumination settings.